Field of the Invention
The invention relates generally to magnetoresistive tunnel junctions (MTJs) and particularly to reliability thereof.
Description of the Prior Art
Magnetoresistive tunnel junctions (MTJs) show future promise in replacing the position today's random access memories (RAMs) enjoy for a number of reasons among which is their considerably smaller size and greater speed. However, challenges remain in producing reliable MTJs, particularly in volumes. Designers and manufacturers struggle with the consistent and reliable programmability and sensing of MTJs. Their small form factor is of no help and rather causes challenges such as providing sufficient voltage and current for proper operability of MTJs yet not exceeding the level of current to the point of causing permanent damage. This may seem like a trivial task but in reality, when working on an very small level, reaching a sweet spot range can be a challenging task in and of itself.
As a fall out of MTJ's programming characteristics, current requirements decrease when temperature rises. When programmed with excessive current, MTJs are placed in danger of being permanently damaged.
There is a phenomenon known as “hopback” that occurs due to intolerable current levels where programming the MTJ to a certain logical state that causes the MTJ to take on a high resistance results in the programming of the MTJ to a state represented by a low resistance instead. Clearly, this outcome is unacceptable. Another outcome of higher-than-necessary current flow through a MTJ is unnecessary power consumption. One way of overcoming the problems associatd with an undesirable increase in current at high temperatures is to control the level of current through the MTJ and compensate at different temperatures. But to do so requires the use of a current source that uses considerably higher voltages than that required by MTJ and is therefore impractical.
Thus, there is a need for reliable programming and sensing of MTJs at different temperatures.